PROJECT SUMMARY: Project 1 The focus of Project 1 is to increase our understanding of the pathogenesis of norovirus infection and to develop treatment and prevention strategies that can be applied to infected and at risk populations. Human noroviruses are the most common cause of epidemic and sporadic gastroenteritis in the United States, causing both significant health and economic impact, but we currently have only non-specific measures to prevent and treat infection. Our prior research has shown that persons with serum antibody that blocks binding of viral particles to putative glycan attachment factors have decreased risks of illness and infection after exposure to virus, and that following infection such blocking antibodies can develop against heterologous strains. Nevertheless, a major potential barrier to vaccine development is the significant genetic and antigenic variation that occurs. Chronic infection among immunocompromised patients has been proposed as one source of emergent variants. We hypothesize that infections in children and elderly individuals are another source of viral variants. In Specific Aim 1 we will determine whether the frequency of emergent variants is greater in children or the elderly compared to immunocompetent adults, and the frequency of these variants will be contrasted with that observed in an immunocompromised population. The potential impact of genetic changes on VP1 structures (e.g., in histoblood group antigen binding specificities) will be assessed in collaboration with Project 3. Viral strains collected in this project will also be used in cultivation studies in Project 2. In Specific Aim 2, we will perform studies to better understand the humoral immune response induced following infection. We will test the hypothesis that the generation of antibody responses to genotypes distinct from the infecting strain is more common in immunocompetent adults than in children. Human monoclonal antibodies will be made by cloning the heavy and light chain variable domains from plasmablasts generated during acute infection, and expressing these in combination with immunoglobulin constant domains. Antibody reactivity and the ability of the antibodies to block virus-glycan interactions against homotypic and heterotypic strains will be determined. Antibodies that block virus-glycan interactions for a large number of genotypes may have value for use in prophylaxis of risk groups. In Specific Aim 3, we will use an integrated strategy including structure-based inhibitor design, synthetic medicinal chemistry, structure activity relationship analysis, and toxicological studies to develop and characterize antivirals targeting the viral protease. Structural information about key inhibitors developed in this aim will be obtained in collaboration with Project 3. Monoclonal antibodies and antiviral agents developed in Aims 2 and 3 will be evaluated for activity in RNA expression and replication systems developed in Project 2. Overall, these studies are designed to understand and evaluate the importance of age and immune status on virus variation and on the development of potential humoral immunity and to develop reagents that can be used to prevent or treat norovirus infection.